This invention relates to angiography and more specifically, the injector used to inject a medical fluid such as radiographic contrast material into living organisms.
One of the major systems in the human body is the circulatory system. The major components of the circulatory system are the heart, blood vessels, and the blood, all of which are vital to the transportation of materials between the external environment and the different cells and tissues of the human body.
The blood vessels are the network of passageways through which the blood travels in the human body. Specifically, arteries carry the oxygenated blood away from the left ventricle of the heart. These arteries are aligned in progressively decreasing diameter and pressure capability from the aorta, which carries the blood immediately out of the heart to other major arteries, to smaller arteries, to arterioles, and finally to tiny capillaries, which feed the cells and tissues of the human body. Similarly, veins carry the oxygen depleted blood back to the right atrium of the heart using a progressively increasing diameter network of venules and veins.
If the heart chambers, valves, arteries, veins or other capillaries connected thereto are either abnormal (such as from a birth defect), restricted (such as from atherosclerotic plaque buildup), or deteriorating (such as from aneurism formation), then a physician may need to examine the heart and connected network of vessels. The physician may also need to correct any problems encountered during the examination with a catheter or similar medical instrument.
Angiography is a procedure used in the detection and treatment of abnormalities or restrictions in blood vessels. During angiography, a radiographic image of a vascular structure is obtained by injecting radiographic contrast material through a catheter into a vein or artery. The vascular structures fluidly connected with the vein or artery in which the injection occurred are filled with contrast material. X-rays are passed through the region of the body in which the contrast material was injected. The X-rays are absorbed by the contrast material, causing a radiographic outline or image of the blood vessel containing the contrast material. The x-ray images of the blood vessels filled with contrast material are usually recorded onto film or videotape and are displayed on a fluoroscope monitor.
Angiography gives the doctor an image of the vascular structures in question. This image may be used solely for diagnostic purposes, or the image may be used during a procedure such as angioplasty where a balloon is inserted into the vascular system and inflated to open a stenosis caused by atherosclerotic plaque buildup.
Currently, during angiography, after a physician places a catheter into a vein or artery (by direct insertion into the vessel or through a skin puncture site), the angiographic catheter is connected to either a manual or an automatic contrast injection mechanism.
A simple manual contrast injection mechanism typically has a syringe and a catheter connection. The syringe includes a chamber with a plunger therein. Radiographic contrast material is suctioned into the chamber. Any air is removed by actuating the plunger while the catheter connection is facing upward so that any air, which floats on the radiographic contrast material, is ejected from the chamber into the air. The catheter connection is then attached to a catheter that is positioned in a vein or artery in the patient.
The plunger is manually actuated to eject the radiographic contrast material from the chamber, through the catheter, and into a vein or artery. The user of the manual contrast injection mechanism may adjust the rate and volume of injection by altering the manual actuation force applied to the plunger.
Often, more than one type of fluid injection is desired, such as a saline flush followed by the radiographic contrast material. One of the most common manual injection mechanisms used today includes a valve mechanism which controls which of the fluids will flow into the valving mechanism and out to the catheter within the patient. The valve mechanism contains a plurality of manual valves that the user operates manually to open and close that particular fluid channel. When the user suctions or injects contrast fluid into the chamber, the fluid is pulled from the valve mechanism via the open valves. By changing the valve positions, another fluid may be injected.
These manual injection mechanisms are typically hand actuated. This allows user control over the quantity and pressure of the injection. However, all of the manual systems are only capable of injecting the radiographic contrast material at maximum pressure that can be applied by the human hand (i.e., 150 p.s.i). Also, the quantity of radiographic contrast material is typically limited to a maximum of about 12 cc. Finally, there are no safety limits on these manual contrast injection mechanisms which act to restrict or stop injections that are outside of reasonable parameters (such as rate or pressure) and no active sensors to detect air bubbles or other hazards.
Currently used motorized injection devices consist of a syringe connected to a linear actuator. The linear actuator is connected to a motor, which is controlled electronically. The operator enters into the electronic control a fixed volume of contrast material to be injected at a fixed rate of injection. The fixed rate of injection consists of a specified initial rate of flow increase and a final rate of injection until the entire volume of contrast material is injected. There is no interactive control between the operator and machine, except to start or stop the injection. Any change in flow rate must occur by stopping the machine and resetting the parameters.
The lack of ability to vary the rate of injection during the injection results in suboptimal quality of angiographic studies. This is because the optimal flow rate of injections varies considerably between patients. In the cardiovascular system, the rate and volume of contrast injection is dependent on the size of and blood flow rate within the chamber or blood vessel being injected. In many or most cases, these parameters are not known precisely. Moreover, the optimal rate of injection can change rapidly, as the patient's condition changes in response to drugs, illness, or normal physiology. Consequently, the initial injection of contrast material may be insufficient in flow rate to outline the structure on x-ray imaging, necessitating another injection. Conversely, an excessive flow rate might injure the chamber or blood vessel being injected, cause the catheter to be displaced (from the jet of contrast material exiting the catheter tip), or lead to toxic effects from contrast overdose (such as abnormal heart rhythm).
At present, the operator can choose between two systems for injecting contrast material: a manual injection system which allows for a variable, operator interactive flow rate of limited flow rate and a preprogrammed motorized system without operator interactive feedback (other than the operator can start/stop the procedure).